[PATCH] mm: lock newly mapped VMA with corrected ordering

[Hugh Dickins]

Lockdep is certainly right to complain about
(&vma->vm_lock->lock){++++}-{3:3}, at: vma_start_write+0x2d/0x3f
               but task is already holding lock:
(&mapping->i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db
Invert those to the usual ordering.

Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after it 
becomes visible")
Cc: sta...@vger.kernel.org
Signed-off-by: Hugh Dickins <hu...@google.com>
---
 mm/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 84c71431a527..3eda23c9ebe7 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2809,11 +2809,11 @@ unsigned long mmap_region(struct file *file, unsigned 
long addr,
        if (vma_iter_prealloc(&vmi))
                goto close_and_free_vma;
 
+       /* Lock the VMA since it is modified after insertion into VMA tree */
+       vma_start_write(vma);
        if (vma->vm_file)
                i_mmap_lock_write(vma->vm_file->f_mapping);
 
-       /* Lock the VMA since it is modified after insertion into VMA tree */
-       vma_start_write(vma);
        vma_iter_store(&vmi, vma);
        mm->map_count++;
        if (vma->vm_file) {
-- 
2.35.3